1. MEMS Tuning-Fork Gyroscope Group 8: Amanda Bristow Travis Barton Stephen Nary

2. What is a MEMS Gyroscope? ● A small, silicon device that senses rotation ● Benefits: ● Small size ● Low power ● Cheap to mass produce MEMS Gyroscope viewed under a microscope

3. Where is it Used? iPhone 4 Wii Motion Plus ● Used in devices requiring detection of rotational motion: ● IPhone 4 ● Wii Motion Plus accessory

4. Purpose ● To refine an existing MEMS Gyroscope design to improve accuracy ● To examine the method of fabrication for MEMS devices ● To gain practical experience with the testing of MEMS devices using the existing design

5. Structure of a MEMS Gyroscope Drive electrode Sense electrodes Anchors Proof mass Drive electrode ● Symmetric mechanical structure ● Gyroscope structure free to move, except at anchors ● Comb Drive Transducers used to drive proof masses ● Sense electrodes used to detect rotation Gyroscope Structure

6. Drive Mode ● Structure made to vibrate at natural frequency ● Vibration of proof mass provides necessary velocity for Coriolis Acceleration Drive Mode Vibration

7. Sense Mode ● When rotation is applied, Coriolis force causes proof mass direction to change Coriolis Acceleration Sense Mode Vibration

8. Optimization of Mechanical Structure ● Ideal frequency range: 15 kHZ – 30 kHz ● Ideal difference between drive mode and sense mode: 50 Hz – 100 Hz ● Key Dimensions for adjusting frequency: ● L2 → Sense Mode ● L1 → Drive Mode L2 L1 Key Dimensions

9. Optimization of Mechanical Structure TrialL1, μmDriveL2, μmSenseDifference 453014598.07562015888.0531289.978 552014924.58762015904.967980.381 651015281.02862015922.051641.023 750015653.75062015942.423288.673 849915694.66562015943.953249.289 949815730.41262015944.225213.813 1049715759.22362015944.581185.358 1149615809.87162015947.541137.670 1249515832.34562015948.254115.910 1349415872.90662015951.40178.495 1449315911.84062015953.96742.127 1549215951.37962015951.9310.552

10. Optimization of Mechanical Structure

11. Comb Drive Transducers Drive electrode Anchors Proof mass Drive electrode ● Form capacitors with proof masses ● Use “fingers” to increase surface area ● AC voltage applied to one transducer to excite proof masses to vibrate ● Other transducer used to monitor drive mode vibration Comb Drive Transducers

12. Designing the Comb Drive Transducers V DC ~ v AC Voltage Sources Proof Mass Vibration Amplitude Magnified View: Proof Mass and Comb Drive Fingers

13. CAD Model for Mask - Calculations determine structure dimensions - Total of 25 fingers on proof mass - 2 micron interference for comb transducers - 3 micron sense gap

14. Manufacturing of MEMS Gyroscope 1. Design is laser etched onto a chrome plated mask. 2. Align mask above silicon wafer. 3. Expose wafer and mask to UV light. Mask Photo resist Silicon substrate Mask Photo resist Silicon substrate

15. Manufacturing of MEMS Gyroscope 5. Developing

16. Mechanical structure needs to move freely. Therefore special wafer is used. 6. Etch SiO2 Note: HF does not etch away all SiO2 Manufacturing of MEMS Gyroscope

17. Planned Work ● Complete Sense Mode Calculations ● Complete AutoCAD drawing for gyroscope die ● Connect PCBs for testing ● Learn testing procedure ● Learn to interpret data PCB

18. Questions?